Atlas Mountain Range Floats on Layer of Molten Rock

The Atlas Mountains in Morocco are structurally different from mountains of similar height, according to new research which suggests that rather than being rooted dozens of miles beneath the surface, the mountains are buoyed up by superhot rock.

The Atlas range defies the standard model for mountain structure, which suggests that the taller the mountain is, the deeper it must be rooted in the earth. In this new model, the researchers contend that the Atlas Mountains instead float on a layer of hot molten rock that flows beneath the region's lithosphere, which is the outermost layer of the Earth.

"Our findings confirm that mountain structures and their formation are far more complex than previously believed," said lead author Meghan Miller, assistant professor of Earth sciences at the University of Southern California (USC).

In geology, the term istostacy refers to the concept that the height of the Earth's crust must supported by commensurate depth, much like an iceberg doesn't simply float atop the water, but instead rests on a larger submerged mass of ice.

USC's Thorsten Becker, a professor of earth sciences and a research co-author, spoke of the discrepancy in istostacy observed on the Atlas range.

"The Atlas Mountains are at present out of balance, likely due to a confluence of existing lithospheric strength anomalies and deep mantle dynamics," he said.

For their research, Becker and Miller used 15 seismometers placed at various points around the Atlas Mountains to measure the depth and thickness of the region's lithosphere. By collecting data produced by the region's seismic events, the researchers were able to plot a graph that gives an "image" of what the deep subsurface beneath the Atlas Mountains looks like.

Although the elevation of the Atlas Mountain range exceeds 4,000 meters - its tallest peak, Toubkal is 4.165 meters - the crust beneath the range only 35 kilometers deep, which is about 15 kilometers shy of what's predicted by standard lithospheric models.

"This study shows that deformation can be observed through the entire lithosphere and contributes to mountain building even far away from plate boundaries" Miller said.

The research was published in the journal Geology on Jan. 1.